Add message to see troubleshooting page when render engine fails to initialize

[iche033]

🦟 Bug fix

Summary

Instructs the user to visit https://gazebosim.org/docs/fortress/troubleshooting when render engine fails to initialize. There is already some information on the page about issues creating the render window. I plan to add a little more info that page.

We'll need to update the url when merging forward.

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

[codecov]

Codecov Report

Merging #793 (d48fb5c) into ign-rendering6 (b3df123) will decrease coverage by 0.03%.
The diff coverage is 70.00%.

@@                Coverage Diff                 @@
##           ign-rendering6     #793      +/-   ##
==================================================
- Coverage           77.85%   77.82%   -0.04%     
==================================================
  Files                 146      146              
  Lines               13404    13412       +8     
==================================================
+ Hits                10436    10438       +2     
- Misses               2968     2974       +6     

Impacted Files	Coverage Δ
ogre2/src/Ogre2RenderEngine.cc	78.29% <0.00%> (-0.53%)	⬇️
ogre2/src/Ogre2Camera.cc	87.86% <25.00%> (-1.49%)	⬇️
ogre2/src/Ogre2DepthCamera.cc	88.37% <100.00%> (ø)
ogre2/src/Ogre2GpuRays.cc	95.52% <100.00%> (+<0.01%)	⬆️
ogre2/src/Ogre2RenderTarget.cc	86.33% <100.00%> (ø)
ogre2/src/Ogre2SelectionBuffer.cc	93.06% <100.00%> (ø)
ogre2/src/Ogre2ThermalCamera.cc	88.60% <100.00%> (ø)

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